Immunotherapy represents one of the most promising therapeutic modalities for cancer. However, the immune responses induced by current immunization approaches are generally insufficient to generate adequate clinical responses. Development of effective immunization approaches ultimately require rational designs based on detailed knowledge of how immune cells are activated. The antigen presenting function of DCs as whole population is well established, but the role of each distinct DC subset has not been defined but is critical for developing targeted effective immunization approaches. In this proposal we will focus our effort on understanding the roles of the different DC subsets in lentivector mediated genetic immunization and the mechanism of how T cell immune response is elicited. We hypothesize that cutaneous administration of lentivector will result in specific transduction of skin DCs (sDCs) and direct priming of naive T cells, which can exploited for designing more effective antitumor genetic immunization strategies. The specific Aims are as follows: Aim 1: To investigate the mechanism of T cell priming in lentivector immunization;Aim 2: To manipulate antigen processing pathways to elicit more effective T cell responses;and Aim 3: To evaluate the antitumor effectiveness of lentivector immunization. To accomplish these aims, DC subsets from lentivector immunized mice will be examined for their function of priming naive T cells ex vivo and in vivo. The mechanism of direct vs cross priming of naive T cells will be determined in vivo. In addition, the potential of utilizing lentivector immunization in inducing T cell immune responses against self tumor antigen will also be investigated. Promotion of endogenous antigen processing by ubiquitin mediated degradation pathway and exogenous antigen presentation by Fc receptor will be investigated to enhance T cell responses against melanoma self tumor Ag TRP-2. Our study will yield information pertinent to DC subsets that activate T cells in vivo, the mechanism how T cell are primed in vivo, and the potential of lentivector immunization in eliciting T cell responses against self tumor Ag. The knowledge gained from these studies will assist the design of more effective and safer genetic immunization approaches for antitumor immunotherapy.